Means for forming sheet metal



March 5, 1946; H. M. JAGER ET AL 2,395,330

' MEANS FOR FORMING SHEET METAL Filed No). 3, 1942 Patented Mar. 5, 1946 Howard M. Jager, Oceanside,

and Edouard Schenk, New York, N. Y., assignors to Republic Aviation Corporation, a

aware corporation of Del- Application November 3, 1942, Serial N 0. 464,356 '1 Claims. (01. 153-48) The present invention has to do with forming sheet-metal into various hollow shapes, and this application is similar in some respects to the patent to'Howard M. Jager, No. 2,378,482, dated June 19, 1945.

Although the present invention, like that of said patent, also relates generally to a means for forming sheet metal by applying a novel clamping action to the sheet while stretch-forming the sheet, the present invention is particularly concerned with forming flat sheets of metal into hollow bodies that are considerably thinner, or of lesser cross-section, than those that could be dealt with in the machine of said patent, and in addition, having taper at each end, instead of at only one end; that is to say, instead of being of constricted shape at only one edge or end, they are constricted at both edges or ends.

More specifically, this invention has especial reference to forming such relatively shallow, fiat, extensive,hollow, curved metal bodies as aircraft fins, rudders, flaps, ailerons, elevators, stabilizers and the like. In forming such articles by employing the general principles of said'application and said invention, it is contemplated by the present invention to apply the stretching-force in a different manner and position; to providea difierently-acting clamping force, located in a different position; and to provide different means for permitting insertion of the work-sheet in a different manner in the machine, from the modes and means disclosed in said application and it is one of the objects of this invention to make these provisions.

The other objects of, and results achieved by,

the invention will become manifest as this disclosure proceeds.

One form of embodiment of the inventive concepts is shown in the accompanying drawing, and described hereinafter, by way of example, only; and it is to be understood that the invention is limited in its embodiments only by the scope of the sub-joined claims.

In the drawing:

Figure l is a fragmentary side elevation of a sheet-metal forming machine embodying the present invention;

Figure 2 is an enlarged end-view, partly in section, along line 22 of Figure 1, and

Figure 3 is an enlarged section along line 3-3 of Figure 1, showing the parts in another position.

The stretching machine is shown as applied to form the s of the leading or hinge edge of an aircraft rudder and includes a stationary lower form' block 22, in the lower portion of w l' lch is formed a central recess defining two legs 22' extending longitudinally of the block. This block 22 is provided'with two opposed end-ears 23 resting in corresponding self-aligning seats 24' 'formed in a pair of H-shaped uprights 24 forming part of a support or operating table 25, 26.

Before it is processed therein, the metal sheet to be formed is bent in a compound bend along its opposed longitudinal edges in such manner as to form two U-channelled retaining borders. It

is then fitted over an upper movable form-block 2| of the machine, which block rests on the staslanting sides of the wedge l0, instead of but one side, cooperate with the inner faces of said legs 22' toclamp the upturned wings of the U-channels formed along the edges of the work sheet 20. In the present invention also, there are tightening devices, but herein take the form of studs 12, having opposed heads l3, I4. Through holes in the lower heads l4 passes a longitudinal shaft l5 made in two parts, each part carrying a plurality of cams or eccentrics l6, fixed on the shaft l5 by means of keys IT. The two halves of the shaft [5 may be operated simultaneously by means of a pair of opposed handles I9, slidably mounted across hubs'l8 fixed onthe opposed outer ends of the'shaft parts l5. 7

The upper movable block 2| can be spread apart from the lower block 22, with the sheet of metal engaged around the top, by means of a hydraulic jack schematically shown as a power unit fitting within a corresponding elongated hole formed half in' the block 2| and half in the block 22; This power unit comprises an elongated hydraulic chamber 28 preferably of U-section housed in the fixed block 22 andan elongated plunger 29, the head of which is similarly housed in the movable block 2|. An operating fluid 30, preferably oil, is admitted into the chamber 28 through conduits (not shown) Each clamping assembly, including elements Hl--l9, rests freelyon the table 25, 28 when the machine is at rest, (as in Figure 1) and is car tions along said extensions by means of cco'per-' ating slanting guiding surfaces 21, 3| so as to clear the two lateral entrances for said channelled edges provided between each of thelegs 22 and the corresponding longeron 25 of the table 25, 26. f

Normally, there is no fluid; the chamber 28;

and the movable block 2! rests upon the fixed block 22. When it is desired to put a work sheet in position on the form 2 l ;-22,-the two clamping;

assemblies, In to iii, are first withdrawn from of the twoU-channelsand the eccentrics ware simultaneously turned the-desired angle so as tqwedgethe gang nut l0 againstsaid wings and pressthelowerjaw ll upagainstthe bottom of then-channels. 7 j V n Thus anchored to the fixed part 220i the machine gthe work sheet 29 can be stretched beyonditselastic limit and, .permanent1y deformed-into the desired shape, by applying pressure fluid, thus being given a permanent deiorrnationwithout having to carefully control the pressure applied, as the upturned edges of the sheet. Ml-will merely slipoutoi theclamp if this pressurereaches a value above the ultimate tensile strength of said sheet, instead of excessive stretching forces tearing the sheet, as was usually h r i ne the 631 1. V

Byhaving interchangeable blocks 2!, 22 of varying shapes andlengthsit is possibleito use the machine for forming a great variety of shallow skin sections oi-aircraft structures, and by interpgsing shims 33 between the upper heads 13 ct the studs I2 and the wedges II), it becomes possible to form sheets of different gage without having to make any change or adjustmentin-the machine. It is; to be noted, that, as there is no vibration in the machine duringits operation, the clamping assemblies 18 to H1 can be, andvare, sch-locking;

V Afterthe sheet 26 1 thus stretched to the desired extent and-formed, thehydraulic pressure is releasedand the two opposed handles. 19 are turned-in order to loosen the clamp. The block 2| then falls fromthe operative position shown infiigure 3 intothe inactiveposition shown in Figure 2, while.the plates fall on the table 25, 2G, and the wedges -Hl are vlifted by the action of the springs 32,;thereby freeing the "sheet 29, which canthen be easily removed endwise from the grippingjawslfl, ll and 2:2, I

. The retaining channels of the skin section thus obtainecig a after this removal, either fbe trimmed away,- or .-be retained as reinforced edges; which may later on, when assembled with, the usual;,transN? sal ribs and a longitudinal web riyetediiq the bottom {ii-these, channels-f01n1 thev spar of; an aircraft or other structure, such, asoi, a fin, flap or the like.

longitudinal edges of the sheet closely adjacent each other in .J'uxtaposition in such manner as to form thereby,a'single continuous force-absorbing-c structure thereat, the forming-zone consis ing of two internally separable blocks in juxtaposition with each other, over which the sheetmetal is stretched by internal expansion. The work member is thus arranged to substantially completely envelop the entire stretching zone or forming dies, in which zone the tensile force is applied by separating the dies by internal expansion, The expansion isachieved by automatic power means and thelblocks form a compact form-unit" which unit maybe varied in size, atwill, by interchanging with blocks of other sizes. In operation, the work itself forms an oil seal at the increasing gap between the members 2! and 22; Insertion of fresh work sheets is also facilitated and rendered easier than heretofore, by these means, and yet the original advantages of'the foregoing machine are retained withal,

Having thus .disclosedfthe, inventive concepts and one embodiment thereof, what is claimed is:

1., In a machine of the type described; a base; av form-group mounted, thereon, thelower part of the form having .a reeesstherein; a wedgemember mounted in said recess; said Wedge having spaced apertures therein; a plate mounted on said base adjacent said recess and having corresponding apertures therein; a. plurality of double-acting fastening members mounted to extend thru said apertures to join the wedge and plate; a shaft rotatably mounted in the lower ends oi said fastening members a plurality of eecentrics mounted onsaid shaft: and means for rotating said shaft} c;

2. In a machine for stretching sheet metal into hollow forms the combination with a pair of separable superposed die members to be enveloped by a work sheet, one of said members havin a groove in its under face with upwardly divergent walls, of a movable wedgemember coextensive with said groove having its sides convergent to lie substantially parallel to the walls of said groove regardless or its position within the groove, an external. clamping jaw opposed and parallel to the grooved face aforesaid, and a connection between said wedge, member and said external jaw whereby theymay be moved 'simultaneously toward one another to engage the edges of the work sheet between the sidesfoi'the wedge and the walls of the groove at. the same time and clamp portions of the work sheet adjacent its engaged edges between the external jaw and the grooved die face upon each side'of-said groove;

i 3'. In a machine for stretching sheet metal into hollow forms the combination with apairof separable superposed die members to be enveloped by a Work sheet the lower of said members being stationary and having a relatively flat unf sur ace with afig oove centrally positioned therein for receiving the Opposed edges of the work sheet, the walls whereof diverge upwardly, of a; wed e member x e i e ith: ns gmm' vertically in 'saiii*emqrcfhavine lts sids' b 7s vergent to rest substantially parallel to mavens of said groove regardless of its Position within the groove, an external clamping jaw opposed and parallel to the under grooved face aforesaid, and a connection between said wedge member and said external jaw whereby they may be moved simultaneously toward one another to clamp the edges of a work sheet enveloping both die mem-' bers between the sides of the wedge and the walls of the groove and thos portions of the work sheet adjacent to the clamped edges between the external jaw and said grooved under face upon each side of said groove. I

4. In a machine for stretching sheet metal into hollow forms, the combination with a pair of superposed separable die members the work faces of which converge in opposite directions, power means for moving said die members in opposite directions against a work sheet entirely enveloping and resting flush against the work faces thereof, the lower of said die members having a relatively fiat outer surface provided with a central groove the walls of which diverge upwardly, a wedge member movably positioned Within and coextensive with said groove the sides of which converge to lie always parallel to the walls of the groove, an external clamping jaw parallel to the aforesaid fiat outer surface, connections between said wedge member and said external jaw permitting relative movement thereof, and means to move said jaw and said wedge member simultaneously toward each other whereby the extreme edge portions of a work sheet enveloping said die members are engaged between the sides of the wedge and the walls of the groove while those portions of the work sheet adjacent the extreme edge portions are independently clamped between the movable jaw and the flat outer surface aforesaid upon each side of the groove there- 5. In a machine for stretching sheet metal into hollow forms the combination with a pair of superposed separable die members the work faces of which converge in opposit directions, power means for moving said die members in opposite directions against a work sheet entirely enveloping and resting flush against .the work faces of said die members, the lower of said die member having a relatively flat under surface for cooperation with the opposededge portions of a work sheet enveloping said members and provided with a central substantially coextensive groove the walls of which diverge upwardly, a wedge member movably positioned within said groove and coextensive therewith having its walls convergent to lie always parallel to the walls of the groove, an external clamping jaw parallel to the fiat surface aforesaid, connections between said wedge member and said external jaw, springs interposed between said wedge member and said external jaw tending to separate them, and means for moving said jaw and wedge one toward the other against the action of said spring whereby the extreme edge portions of the work sheet are engaged between the sides of the wedge and the walls of the groove while those portions of the work sheet adjoining said extreme edge portions are independently clamped between the movable jaw and the flat surface aforesaid upon each side of its groove.

6. In a machine for stretching sheet metal into hollow forms, the combination with a pair of separable die members, the work faces of said die members converging in opposite directions and one of said members having a base of less width than the greatest width of either of said die members, and a single means associated with said base for clampingly engaging the opposed edge portions of a work sheet completely enveloping said 

